Polyvinylidene fluoride (PVDF) films possess the highest values of piezoelectric and pyroelectric constants of any known polymer. PVDF is semicrystalline and contains at least two stable forms, a polar form I containing .beta.-crystallites and a non-polar form II containing .alpha.-crystallites. The .beta.-form has an extended all-trans (planar zig-zag) polar conformation. The .alpha.-form has a trans-gauche-trans-gauche' (T-G T-G') non-polar conformation. Uniaxial stretching and subsequently subjecting these films to high electric elevated temperature converts the .alpha.-crystallite to the .beta.-form and aligns dipoles giving rise to large polarizations.
It has been assumed, up to present, that saturation of the polarization of these films is obtained by first stretching the films and subsequently subjecting them to corona poling. If both sides of these films are metallized and A.C. voltages applied, the films will vibrate due to the piezoelectric effect. If the temperature of these metallized films is raised, a current output will be obtained due to the pyroelectric effect. The converse of these later two statements also applies. The maximum values for the piezoelectric constant (d.sub.31) and pyroelectric constant (p) that so far have been reported with these type of films are 30-35 pC/N and 3.5nC/cm.sup.2 K respectively where C is Coulombs, N is Newtons and K is degrees Kelvin.